Some engine systems may employ exhaust braking to decrease a speed of a vehicle in motion. As used herein, the term “exhaust braking” means a process for reducing a speed of a vehicle by increasing the pumping losses of an engine. The term “pumping losses” means the negative work done on an engine. In turn, the term “negative work done on an engine” means work that is in a direction opposite to the displacement of a piston of the engine. Accordingly, the negative work done on an engine may reduce the engine speed.
Exhaust braking may be performed, for example, by obstructing a flow of exhaust gas downstream of an engine such that the exhaust gas is compressed in an exhaust manifold of the engine system in order to generate back pressure in a combustion chamber of the engine. In this disclosure, the term “back pressure” means exhaust gas pressure in a direction from an exhaust port of an engine toward the combustion chamber of the same engine. During exhaust braking, the back pressure causes negative work on the engine.